Stretch cling films are self-adhering films that are used to wrap, fasten and/or protect a variety of items during shipping including palletized goods and new vehicles. Typical stretch-cling film consists of polyethylene impregnated with a low molecular weight tackifier, such as, for example, polyisobutylene. Unwrapping of self-adhering film is either performed manually with hand-held devices or with the use of powered turntable-type wrapping machines or powered unwinding equipment. Unfortunately, regardless of the use or the form of application, high decibel noise is typically generated when self adhering film is unwrapped. In fact, unwrapping noise generally increases as the cling level of the film increases, and commercial stretch-cling wrapping films are particularly notorious for excessive noise generation. For example, unwrapping of commercially supplied stretch-cling films with powered turntable-type wrapping machines typically generates continuous noise in excess of about 90 decibels which exceeds the OSHA standard 1910.95 for permissible workplace noise levels.
The noise associated with unwrapping stretch cling films correlates with the unwrapping take-off angle of the film. In commercial stretch wrapping machinery, when adhesion or cling performance is relatively high, the unwrapping take-off angle of the film will be relatively low during continuous unwrapping operations. For example, for a stretch wrap film having about 140 grams of cling at 200 percent elongation, the unwrapping take-off angle of such film will typically be in the range of about 30 to about 60 degrees and especially less than about 75 degrees.
There are several known approaches for mitigating the high noise levels associated with unwrapping self-adhering films. Known approaches include employing lower tackifier levels or utilizing a generally less effective tackifier such as, for example, a film having cling layers consisting of an ethylene methacrylate (EMA) copolymer having a relatively low methacrylate content or an amorphous polyolefin (APO). Another known approach for reducing high noise levels involves utilizing one-sided cling films rather than two-sided cling films. Still another known approach involves maintaining lower ambient temperatures (air conditioning) at unwrapping facilities which reduces noise by reducing the effective migration of tackifying material to the surface of the film. Another known approach involves utilizing "inherent" cling films characterized as having reduced n-hexane extractables (or higher polymer densities) or less than optimum surface smoothness rather than utilizing inherent films having higher extractable levels, lower densities and/or smoother film surfaces. However, regardless of which film variation is pursued to control unwrapping noise generation, invariably, significant noise reductions are only achieved when the cling performance level of the resultant film is substantially compromised, even to the point of rendering the film only marginally effective as a cling film. Thus, in the prior art, undesirable unwrapping noise has been generally regarded as a necessary trade-off for high effective cling performance.
Whereas attempts to abate unwrapping noise have focused on film modifications, little attention has been given to unwrapping machinery modifications as an approach to abate excessive unwrapping noise. Known unwrapping machinery modifications include rollstock speed control, take-off angle variations and the use of deflectors. However, such machinery modifications pertain to pre-stretching or tensioning of films and generally do not pertain to noise reduction. See, as examples, the disclosures by Redfearn in GB publication 2109722A and Lancaster et al. in U.S. Pat. No. 4,336,679. Known and commercially practiced deflector use and positions, rollstock speed control and take-off angle variations that are allegedly sufficient to achieve desired tensioning levels, are insufficient to effectuate substantial noise reduction during unwrapping operations. For example, commercially available pre-stretch unwrapping machinery must be specifically modified to allow the unwrapping of stretch cling films at noise levels at less than about 95 decibels, especially less than about 90 decibels.
The object of the present invention is to solve the long standing problem of self-adhering films generating excessive noise during unwrapping operations. Another object of the present invention is to achieve substantial noise reduction while maintaining high adhesion or cling performance. Still another object of the present invention is to achieve substantial noise reduction when stretch-cling film is unwrapped and dispensed as either pre-stretched or non-stretched wraps. Unlike prior art approaches that compromise adhesion or cling performance, the present objectives are met by a new method and device that do not require alteration of the cling performance of the film.